Enhanced Safety Nets for En-Route & TMA Operations – SESAR project PJ11 (CAPITO)

The project

The SESAR 2020 Enhanced Air and Ground Safety Nets project is also known as PJ11-CAPITO - Collision Avoidance Performance Improvement TechnOlogy.

CAPITO was launched on 1 November 2016 and is part of the SESAR 2020 Multi Annual Programme Industrial Research & Validation for the period 2016-2019 (Wave 1).


At the end of SESAR 1, two issues still needed to be addressed :
  • adapt ground-based safety nets to trajectory-based operations and new separation modes; and
  • the validation of new Airborne Collision Avoidance System (ACAS) variants in future operations.
Today’s ACAS and ground safety nets performance requirements are based on current modes of separation and do not take into account the future operations identified by the Single European Sky ATM Research Programme (SESAR) concept.  PJ11 CAPITO will study the impact of new separation modes and new categories of airspace users on ground and airborne safety nets. The aim is to adapt ACAS operations to SESAR future trajectory management and new separation modes.
PJ11 will have to allow European perspectives to be presented to the USA FAA ACAS program. This is specifically important for ACAS X as the standards fall under joint EUROCAE/RTCA responsibility. These bodies work together to ensure the global harmonisation and acceptability of ACAS.


PJ11 includes five technical solutions:

1.    Solution one (PJ11-G1): Enhanced Ground-based Safety Nets adapted to future operations.  

PJ11-G1 will evaluate the use of DAPs parameters in Non Transgression Zone (NTZ) safety nets; the improvement of ground-based safety nets performance by taking advantage of the availability of new or more accurate data sources; and the enhancement of the performance of STCA by the use of supplementary information.

2.    Solution two (PJ11-A1): Enhanced Airborne Collision Avoidance for Commercial Air Traffic normal operations – ACAS Xa.  

PJ11-A1 will take advantage of optimised resolution advisories and of additional surveillance data, without significantly changing the cockpit interface. The road to this solution was already started in SESAR 1 and supports the development of a replacement for TCAS II (in collaboration with the FAA) that will resolve more Near Mid-Air Collisions (NMAC) and produce fewer nuisance alerts.

3.    Solution three (PJ11-A2): Enhanced Ground-based Safety Nets adapted to future operations – ACAS Xu.

PJ11-A2 will concentrate on the concept of Airborne Collision Avoidance for Remotely Piloted Aircraft Systems.

It will evaluate the performance and benefits of ACAS Xu within European operations/airspace; ensure that the future standard of the ACAS Xu system (MOPS planned currently for 2020) correctly addresses the operational needs of European airspace/operations as well as the technical aspects raised by European industry; ensure that the ACAS Xu system is compatible with the European definition of Detect And Avoid system/capability.

4.    Solution four (PJ11-A3): ACAS for Commercial Air Transport specific operations - ACAS Xo.

PJ11-A3 will identify the main use cases for ACAS Xo capability within current and future European operations; evaluate the benefits/suitability of the basic ACAS Xo implementation developed by FAA for these European scenarios;
evaluate the opportunity in terms of achievable benefits for a tailored ACAS Xo implementation addressing selected European use cases, and define the relevant technical and operational requirements.

5.    Solution five (PJ11-A4): Airborne Collision Avoidance for General Aviation and Rotorcraft – ACAS Xp.

PJ11-A4 will evaluate the operational benefits achievable by SA+ during mixed equipage encounters; analyse the reusability of specific elements (performance classes, horizontal manoeuvring) introduced in the ACAS Xu solution for GA/R/military users;
define and consolidate the initial European operational requirements as well as the technical recommendations for the ACAS Xp development (to be addressed in Wave 2).


  • Reduction in unnecessary disruption to normal flight by ACAS;
  • Improved collision avoidance risk ratio;
  • Enhanced compatibility with ATC practices;
  • System requirements in line with pilot, ATCO and ANSP expectations to provide airspace users with improved equipment.


EUROCONTROL leads this project so as to support:

  • the European standardisation of the new Airborne Collision Avoidance system for civil transport (ACAS Xa) via validation activities;
  • the safe integration of new airspace users, such as Remotely Piloted Aircraft Systems (RPAS) using the specific ACAS variant (ACAS Xu) and General Aviation via the variant ACAS Xp, into the ATM system;
  • the adaptation of short-term conflict alert (STCA) and airborne collision avoidance systems (ACAS) to SESAR future trajectory management and new separation modes.

STCA/ACAS X interactions will also be studied in SESAR2020 Wave 2 when the development of safety nets in future environments is considered to be stable.

Related projects

  • PJ10 PROSA (Controller tools and team organisation for the provision of separation in air traffic management);
  • PJ18 4DTM (4D trajectory management).

Participating partners

  • LEONARDO (Italy)
  • AIRBUS SAS (France)

Project leader

  • Bill Booth who is also Chair of EUROCAE WG-75, the European group responsible for ACAS standards.

This project has received funding from the SESAR Joint Undertaking under the European Union's Horizon 2020 research and innovation programme under grant agreement No 732996.